1. Field of the Invention
The present invention relates to an electrophotographic apparatus such as a copying machine, a printer, or the like which has an arrangement for checking the developing ability of the apparatus.
2. Description of the Prior Art
Electrophotographic apparatus which employ a wet-type or dry-type two-ingredient developing agent for producing visible images generally have a toner density control means including a toner density sensor for controlling the toner density of the two-ingredient developing agent in order to maintain a constant developing ability. The developing ability of the electrophotographic apparatus is however subject to a change due for example to the deterioration of the toner density sensor or the deterioration of the two-ingredient developing agent, resulting in degraded image quality. It is therefore necessary to check the developing ability and remove any change in the developing abiltity when it varies. In checking the developing ability, a skilled engineer can immediately determine a failure of the toner density sensor and control or a deterioration of the two-ingredient developing agent from a visible image which has been developed. However, general users have difficulty in pinpointing which image forming process is responsible for changes in image quality simply by looking at the developed image.